The present invention relates generally to a compound bond layer formed by a selenidation reaction. The compound bond layer adhesively bonds two or more substrates to each other. More specifically, the present invention relates to a polycrystalline or an amorphous compound bond layer formed by a selenidation reaction and including a first multi-stacked layer of selenium and indium or selenium-tellurium and indium formed on a bonding surface of an active substrate and a second multi-stacked layer of selenium and indium or selenium-tellurium and indium formed on a mounting surface of a base substrate. The resulting compound bond layer adhesively bonds the active substrate and the base substrate to each other without having to apply pressure to achieve the bonding and the compound bond layer can be dissolved so that the active substrate and the base substrate can be non-destructively detached from each other.
It is well known in the microelectronics art to use wafer bonding to bond one wafer to another wafer in order to efficiently manufacture complementary metal-oxide semiconductor (CMOS) circuitry or to fabricate micromachined structures such as Microelectromechanical Systems (MEMS). Prior wafer bonding process include silicidation, oxidation such as in a silicon-on-insulator (SOI) wafer bond, and metal hot pressing.
FIGS. 1a through 1c illustrate a prior silicidation wafer bonding process 100 In FIG. 1a, a Wafer A that is to be bonded to a Wafer B has a metal M deposited on a surface thereof. Alternatively, the metal M could be deposited on a surface of Wafer B. The metal M can be a metal such as tungsten (W) and wafers (A, B) can be silicon (Si) wafers. Next, in FIG. 1b, the wafers (A, B) are urged in to contact with each other and pressure P and heat H are applied to effectuate a silicidation reaction. The surfaces of the wafers (A, B) that are in contact with the metal M define an interface i. Typically, the heat H is in the range of about 300 degrees centigrade to about 450 degrees centigrade. Finally, in FIG. 1c, the silicidation reaction has proceeded to completion with the metal M reacting with the wafers (A, B) and diffusing beyond the interface i and into the material of the wafers (A, B) to form a metal silicide M+W. For example, if the metal is tungsten (W) and the wafers (A, B) are silicon, then the metal silicide M+W is WSi.
FIGS. 2a through 2c illustrate a prior oxidation wafer bonding process 200. In FIG. 2a, a Wafer A that is to be bonded to a Wafer B has a dielectric material D deposited on a surface thereof. Alternatively, the dielectric material D could be deposited on a surface of Wafer B. Typically, the dielectric material D is silicon oxide (SiO2) and wafers (A, B) are silicon (Si) wafers. Next, in FIG. 2b, the wafers (A, B) are urged in to contact with each other and pressure P and heat H are applied to effectuate a bonding of Wafer A to Wafer B. The surfaces of the wafers (A, B) that are in contact with the dielectric material D define an interface i. For the oxidation wafer bonding process 200, the heat H can be in a range of about 700 degrees centigrade to about 900 degrees centigrade. Finally, in FIG. 2c, the bonding is completed and the dielectric material D has not diffused beyond the interface i.
FIGS. 3a through 3c illustrate a prior metal hot pressing wafer bonding process 300. In FIG. 3a, a Wafer A and a Wafer B that are to be bonded to each other have a soft metal S deposited on a surface thereof. For instance, the soft metal S can be gold (Au) and wafers (A, B) can be silicon (Si) wafers. Next, in FIG. 2b, the wafers (A, B) are urged in to contact with each other and pressure P and heat H are applied to effectuate a bonding of Wafer A to Wafer B. The surfaces of the wafers (A, B) that are in contact with the soft metal S define an interface i. The heat H can be in a range of about 400 degrees centigrade to about 500 degrees centigrade. Finally, in FIG. 2c, the bonding is completed and the soft metal S has not diffused beyond the interface i.
There are several disadvantages to the prior wafer bonding processes. First, for CMOS circuitry or other temperature sensitive components such as MEMS structures, the high temperatures (i.e. the heat H) required by the prior wafer bonding process can damage the CMOS circuitry or the MEMS structures. For instance, prior wafer bonding processes can require temperatures in excess of 500 degrees centigrade. CMOS integrated circuits can be damage when exposed to temperatures of about 500 degrees centigrade or more. Moreover, there may be applications yet to be identified that can not tolerate temperatures that are even close to the high temperatures of the prior wafer bonding processes but would non-the-less benefit from wafer bonding techniques. Additionally, heat is also required in the deposition of some bonding materials such as silicon oxide (SiO2). Some applications that are heat sensitive may require a bonding material that can be deposited at low temperatures.
Second, the high pressure (i.e. the pressure P) that is used to urge the wafers into contact with each other can result in breakage, distortion, stress, or damage to the wafers or to the resulting wafer bond.
Third, once the wafers are bonded to each other it is not possible to non-destructively detach the bonded wafers from each other. Therefore, a non-reversible wafer bond precludes situations where it would be desirable to separate the wafers or to salvage the wafers.
Fourth, the prior wafer bonding processes are not amendable to bonding two or more substrates (i.e. two or more of the wafers A) onto a single substrate (i.e. the wafer B). In some application it may be desirable to bond a several substrates onto a single substrate.
Fifth, the prior wafer bonding processes often require that the wafers or substrates to be bonded be made from identical materials or similar materials. For example, in some prior wafer bonding processes the wafers (A, B) must be made from silicon (Si). Therefore, flexibility in selecting the material for the wafers is limited and applications that require different materials for the wafers are not accommodated by the prior wafer bonding processes.
Finally, some prior wafer bonding processes result in the bonding material chemically reacting with the wafers and diffusing into the wafers. In some applications it may be desirable to eliminate any diffusion or interfacial reaction between the wafer and the bonding material.
Therefore there is a need for a bonding process that can be accomplished at temperatures that are much lower than the prior wafer bonding processes so that damage to circuitry or other structures residing on the bonded wafers is eliminated and applications that can only tolerate much lower temperatures can be wafer bonded. Additionally, there is a need for a bonding material that can be deposited at low temperatures. There also exists a need for a wafer bonding process that does not require the application of pressure in order to bond the wafers to each other. Additionally, there exists a need for a wafer bond material that allows for the bonded wafers to be non-destructively detached from each other. There is also a need for a bonding material that will not react with nor diffuse the wafer. Moreover there is a need for a wafer bonding process that allows for two or more substrates to be mounted and bonded to a single substrate. Lastly, there exists a need for a wafer bonding process in which dissimilar substrates can be bonded to each other.
The aforementioned needs are met by the substrate bonding process of the present invention. The high temperature problem is solved by using a selenidation reaction that requires temperatures that are significantly lower than the prior wafer bonding processes. The problems associated with depositing the bonding material at high temperatures are also solved by a choice of bonding materials for the present invention. Those materials can be deposited at a range of low temperatures including room temperature. The substrate bonding process of the present invention does not require the substrates to be urged into contact with each other under high pressure thereby solving the aforementioned problems associated with bonding wafers under high pressure. Additionally, the bonding materials of the present invention allow the bonded substrates to be non-destructively detached from one another by exposing the bonded substrates to a selective etchant that dissolves the bonding materials without harming the substrates. Accordingly, the present invention allows previously bonded substrates to be salvaged, reworked, or recycled. The substrate bonding process of the present invention also accommodates bonding one or more substrates to a base substrate thereby overcoming the limitations of the prior wafer bonding processes that allowed for only one substrate to be bonded to another substrate. Another advantage of the substrate bonding process of the present invention is that the bonding materials allow for dissimilar substrates to be bonded to each other. Therefore, the problem of lack of flexibility in the selection of substrate materials is solved by the present invention. Lastly, the bonding materials of the present invention do not chemically react with nor diffuse into the substrates to be bonded.
Broadly, the present invention is embodied in a method for fabricating a bonded substrate using a selenidation reaction to form a compound bond layer that adhesively bonds at least one active substrate to a base substrate. The compound bond layer includes alternating layers of a first material that includes selenium or selenium and tellurium and a second material that includes indium, gallium, antimony, and aluminum. The first and second materials are deposited at a low temperature on a bonding surface of the active substrate and on a mounting surface of the base substrate. After the alternating layers have been deposited, the substrates are then placed into contact with each other without the need to apply substantial pressure to the substrates. The substrates are then annealed to form the compound bond layer.
In one embodiment of the present invention, the annealing step includes heating the active and base substrates at a temperature ranging from about 200 degrees centigrade to about 300 degrees centigrade.
In another embodiment of the present invention, the first layer includes selenium and tellurium and the annealing step includes heating the active and base substrates at a temperature ranging from about 150 degrees centigrade to about 300 degrees centigrade.
In yet another embodiment of the present invention, the alternating layers of the first and second materials are deposited at a temperature ranging from about 0.0 degrees centigrade to about50.00 degrees centigrade.
In one embodiment of the present invention, the bonded-substrate can be non-destructively detached by exposing the bonded-substrate to a selective etching material that dissolves the compound bond layer so that the active and base substrates are no longer bonded to each other.
In another embodiment of the present invention, the first material and the second material comprise elemental compounds and the annealing step results in those elemental compounds forming a polycrystalline compound bound layer that adhesively bonds the active substrates to the base substrate.
In an alternative embodiment of the present invention, the first material and the second material comprise amorphous compounds and the annealing step results in those amorphous compounds forming an amorphous compound bound layer that adhesively bonds the active substrates to the base substrate.
In yet another embodiment of the present invention, a first amorphous layer is deposited on a bonding surface of an active substrate and a second amorphous layer is deposited on a mounting surface of a base substrate, and the active and base substrates are annealed to form an amorphous compound bound layer that adhesively bonds the active substrates to the base substrate.
In one embodiment of the present invention, a plurality of active substrates are bonded to each other by the compound bond layer to form a three-dimensional stack of active substrates that are bonded to the base substrate by another compound bond layer that can be polycrystalline or amorphous.
In other embodiments of the present invention, the active and base substrates can be made from materials including identical materials, dissimilar materials, a semiconductor material including a semiconductor wafer, a metal material, and a dielectric material.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.